Heretofore, a method of forming a minute resist image on a substrate by applying a positive-working photoresist composition to a substrate to form a resist film, exposing it with radiation such as UV rays, deep UV rays, X rays and electron beams and then developing the resist film, that is, the formation of a minute resist pattern by the photolithography method is well-known. In this photolithography method using the positive-working photoresist composition, 2.38 to 2.50 weight % aqueous tetramethyl ammonium hydroxide or 0.50 weight % or more aqueous sodium hydroxide or potassium hydroxide is used as the developing solution. On the other hand, as the positive-working photoresist composition, a composition comprising an alkali-soluble resin and a quinone diazide group-containing photosensitizer, for example a naphthoquinone diazide-type compound is conventionally and generally used. The positive-working photoresist composition using a novolak-type phenol resin as the alkali-soluble resin and a substituted naphthoquinone diazide compound as the photosensitizer is described in, for example, U.S. Pat. Nos. 3,666,473, 4,115,128 and 4,173,470. In these known positive-working photoresist compositions, the naphthoquinone diazide-type compound as the photosensitizer is used in an amount of usually 15 parts by weight or more, frequently 20 to 30 parts by weight relative to 100 parts by weight of the novolak-type phenol resin. However, when these known positive-working photoresist compositions are used as a photoresist composition and developed with the above-described known developing solution as a developing solution, the high sensitive photoresist particularly for TFT (thin film transistor) indicates poor film retention rate (due to too much reduction in film thickness), so there is near limit to attempt for further improvements in sensitivity of the photoresist. In addition, there arises another problem of high process dependency, that is, the characteristics of resist patterns formed vary significantly when treatment conditions in treatment processes are varied (accordingly, process tolerance is reduced).
For the purpose of conferring high sensitivity on the photoresist, it has been attempted to increase the concentration of an alkali in the developing solution or to prolong the developing time. However, if the concentration of an alkali in the developing solution is increased, the resist on unexposed areas shows significantly poor film retention rate, thus failing to attain sufficient resistance in the subsequent etching step, while if the development time is prolonged, there arises the problem of failing to achieve a sufficient effect on the so-called through-put (treatment efficiency per unit time). Further, it is also proposed to add various low-molecular components as the sensitizer. In this case, sensitivity can be improved, but the unexposed portion is easily dissolved in a developing solution together with an exposed area, resulting in a significant reduction in the film retention rate.
On the other hand, for the purpose of improving the resolution of the resulting resist patterns, it has been proposed to add a wide variety of additives such as surface active agents and organic compounds. Such photoresist compositions comprising surface active agents include those described in Japanese Patent Application Laid-Open (JP-A) Nos. 61-70551, 61-151537, 61-232454 and 62-32454, and those compositions comprising other organic compounds such as hydrocarbons in addition to surface active agents include those described in e.g. JP-A No. 62-232453. These compositions have both advantages and disadvantages, and none of these satisfy practically all of high resolution, high film retention rate and high dimension accuracy.
Under the circumstances described above, the object of the present invention is to provide a positive-working photoresist composition, a developing solution and a photolithography method comprising a combination thereof which can simultaneously achieve high sensitivity, a high film retention rate, high resolution, low process dependency, and a formation of excellent pattern profile, that is, can achieve high sensitivity while maintaining a high film retention rate and can form good patterns having high resolution and low dependency of dimensional accuracy in a photolithography method using a positive-working photoresist.